Quantitative Microbial Risk Assessment of Listeria monocytogenes on Fresh-cut Lettuce and Fresh-cut Cantaloupe

Abstract

The increase in foodborne illness outbreaks associated with fresh and fresh-cut produce can be attributed to ineffectiveness of current handling practices. This study describes the change on concentration of population of Listeria monocytogenes in two popular fresh-cut produces, romaine lettuce, and cantaloupe, from farm to table.

Listeria innocua was used as a surrogate for L. monocytogenes to experimentally evaluate the effectiveness of washing treatments (water and chlorine) and develop growth curves under different storage temperatures (between 5 and 36oC). The findings confirm that both washing treatments were significantly more effective (p<0.05) on reducing L. innocua concentration in fresh-cut romaine lettuce than in cantaloupe. For instance, chlorinated water washing reduced L. innocua population by 0.98 log on fresh-cut romaine lettuce compared to just 0.57 log on cantaloupe rind. Furthermore, the experimental data on L. innocua were used to test three predictive models to describe the growth of L. monocytogenes in both produce. All models (Baranyi and Roberts, Gompertz, and Logistic) provided good fit of the data. However, compared to the Baranyi and Roberts model, both Gompertz and Logistic models overestimated the growth rate at temperatures of 10?C and above. Results demonstrated that these models may be used to estimate the growth in fresh-cut produce during distribution, storage or at the market, and potential growth at a consumer level.

Several scenarios were created to evaluate the impact of decontamination treatments, occurrence of cross-contamination, and temperature abuse on the population of L. monocytogenes. In general, expected annual listeriosis cases associated with fresh- cut cantaloupe were higher (around 17) than with fresh-cut romaine lettuce (<1).The time of consumption of the produce was the biggest issue regarding to ensuring the safety of the fresh-cut produce. Occurrence of temperature abuse and cross- contamination also increased the risk of listeriosis in both products. Among the intervention steps, irradiation treatment was the most effective, with 99.99% reduction on the expected number of annual cases of listeriosis for both produce.